Each year, between 1.6 and 3.8 million people each year suffer a mild traumatic brain injury (TBI) in the US alone. Current diagnosis and return-to-participation guidelines are based on patient symptoms, neurocognitive evaluations, and / or physical performance testing. Many of these diagnostic methods suffer from the problem of being subjective, inaccurate, or requiring baseline (before injury) due to large variations in people's inherent ability to perform in these tests. Thus the timely diagnosis is unavailable for a vast number of patients who suffer mild TBI. This project is aimed at developing an objective diagnosis of mild traumatic brain injury (mild TBI) based on physiologic changes in a patient after injury. The method is based on quantification of well-known physiologic changes after a concussion, i.e. the impairment of autonomic function and altered cerebral blood flow (CBF). The novelty of the proposed approach is the use of a recently-developed analytical framework for the analysis of the CBF velocity (CBFV) waveforms. In contrast to previous methods used before, the proposed approach utilizes the entire shape of the complex CBFV waveform, thus obtaining subtle changes in blood flow changes that are lost in other analysis methods. In Phase I of this project, feasibility of the proposed method will be demonstrated using a small study among high school athletes in the Los Angeles region. The objective of Phase I is to develop metrics that can diagnose TBI among studies with an accuracy of 90% or better. Phase II work will focus on developing a portable diagnostic device with improved accuracy, suitable for use in field applications (outside of hospitals). Successful completion of the proposed work will lead to the development of a portable, objective mild TBI diagnostic that can be used in non-clinical settings, that has the potential to vastly improve TBI patient care in all walks of life.